| 28. 2. 4. Trigger Blocks |
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Triggers are used to define code that is executed when certain actions or events occur. |
The Syntax for Creating a Database Trigger |
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CREATE [OR REPLACE] TRIGGER trigger_name
{BEFORE|AFTER} verb_list ON table_name
[[REFERENCING correlation_names] FOR EACH ROW [WHEN (condition)]]
DECLARE
declarations
BEGIN
pl/sql_code
END;
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verb_list -- The SQL verbs that fire the trigger. |
table_name -- The table on which the trigger is defined. |
correlation_names -- Allows you to specify correlation names other than the default of OLD and NEW. |
condition -- An optional condition placed on the execution of the trigger. |
declarations -- Consists of any variable, record, or cursor declarations needed by this PL/SQL block. |
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SQL> CREATE TABLE to_table
2 (col1 NUMBER);
Table created.
SQL>
SQL>
SQL>
SQL> CREATE OR REPLACE TRIGGER before_statement_trigger
2 BEFORE INSERT ON to_table
3 BEGIN
4 DBMS_OUTPUT.PUT_LINE('Before Insert Statement Level');
5 END;
6 /
Trigger created.
SQL>
SQL> drop table to_table;
Table dropped.
SQL>
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SQL>
SQL> CREATE TABLE to_table
2 (col1 NUMBER);
Table created.
SQL>
SQL> CREATE OR REPLACE TRIGGER before_row_trigger
2 BEFORE INSERT ON to_table
3 FOR EACH ROW
4 BEGIN
5 DBMS_OUTPUT.PUT_LINE('Before Insert Row Level');
6 END;
7 /
Trigger created.
SQL>
SQL> drop table to_table;
Table dropped.
SQL>
SQL>
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